>cin >> length, width;
This doesn't do what you think. A comma is inapproriate, it should be another >> operator:

cin>> length >> width;

>cout << " The total cost will be " << areaR << endl;
>areaR= (length * width);
>cin >> areaR;
>cin >> areaR;
This is nonsensical. The ordering seems goofy. You print areaR before assigning it a suitable value, then fill it with user input twice in a row?